minecraft-announce.c

#include <arpa/inet.h>
#include <semaphore.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <time.h>
#include <unistd.h>

enum log_level {
  LOG_FATAL,
  LOG_MSG,
  LOG_DEBUG
};
enum log_level global_log_level = LOG_MSG;

void log_print(enum log_level lvl, const char *fmt, ...)
{
  va_list args;
  if (lvl > global_log_level) {
    return;
  }
  va_start(args, fmt);
  vfprintf(stderr, fmt, args);
  fprintf(stderr, "\n");
  va_end(args);
  if (lvl == LOG_FATAL) {
    exit(EXIT_FAILURE);
  }
}

#define fatal(fmt, args...) log_print(LOG_FATAL, fmt, ##args)
#define msg(fmt, args...) log_print(LOG_MSG, fmt, ##args)
#define debug(fmt, args...) log_print(LOG_DEBUG, fmt, ##args)

int main(int argc, char **argv)
{
  const char *host = "224.0.2.60";
  const uint16_t port = 4445;
  const int wakeup_seconds = 2;
  sem_t wake = {0};
  struct sockaddr_in addr = {0};

  //const uint8_t buf[] = "[MOTD]Home server[/MOTD][AD]25565[/AD]";
  //const size_t buflen = sizeof(buf);
  char *buf;
  size_t buflen;

  struct timespec ts;
  int ret;

  if (getenv("DEBUG") != NULL) {
    global_log_level = LOG_DEBUG;
  }

  if (argc != 2) {
    fatal("usage: minecraft-announce \"[MOTD]A motd here[/MOTD][AD]<port number, e.g. 25565>[/AD]\"");
  }

  buf = argv[1];
  /* include the '\0' in the length */
  buflen = strlen(buf)+1;

  int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
  if (sockfd < 0) {
    fatal("socket failed errno %d (%s)", errno, strerror(errno));
  }

  memset(&addr, 0, sizeof(addr));
  addr.sin_family = AF_INET;
  addr.sin_port = htons(port);
  ret = inet_pton(AF_INET, host, &addr.sin_addr);
  if (ret != 1) {
    close(sockfd);
    fatal("inet_pton failed errno %d (%s)", errno, strerror(errno));
  }

  clock_gettime(CLOCK_REALTIME, &ts);
  msg("sending \"%s\" to %s:%d every %d seconds",
    buf, host, port, wakeup_seconds);

  /* turn final '\0' into '\n' */
  buf[buflen-1] = '\n';

  while(1) {
    ret = sendto(sockfd, buf, buflen, 0, (struct sockaddr *)&addr, sizeof(addr));
    if (ret < 0) {
      fatal("sendto failed errno %d (%s)", errno, strerror(errno));
    }
    debug("sent %d/%d bytes to %s:%d", ret, buflen, host, port);
    ts.tv_sec += 2;
    ret = sem_timedwait(&wake, &ts);
    if (ret < 0 && errno != ETIMEDOUT) {
      fatal("sem_timedwait");
    }
  }

  return 0;
}